In rolling mills of the above-mentioned type, billets are rolled to rods. Downstream of the rolling mill, shears are arranged. By means of the shears, the rolled rod is cut into sections of predetermined length. The total length of the rolled rod usually is determined by the initial length of the billet, taking into consideration the reductions in cross-section occurring in the rolling stands of the rolling mill. Additionally, sections separated by crop cuts within the rolling mill are taken into account. The accumulated length of the rod which has at a certain point of time exited the rolling mill usually is determined by the circumferential speed of rolls of the last rolling stand of the rolling mill, also taking into account the relationship between the speed of the rod exiting the last rolling stand and the circumferential speed of the rolls of the last rolling stand. For detecting the head end of the rolled rod, a hot metal detector for detecting presence of hot metal is used.
The method of the state of the art is complicated and inexact. In the state of the art, the predetermined length is determined such that the real length of the sections of the rod after cutting off the sections is larger than the minimum length which is the lowest permitted length. The additional length reduces the productivity and efficiency of the rolling mill.